The central theme of this research proposal is the hypothesis that a recently discovered group of intracellular vitamin A-binding proteins plays an important role in the uptake of vitamin A by retinal pigment epithelium (RPE) and its subsequent transfer to and metabolism by the neural retina. The three vitamin A-binding proteins which were discovered in bovine retina during the course of the previous grant period, will be purified to homogeneity and characterized. The molecular relationship of these proteins to each other and to the serum retinol-binding protein will be examined. Methods will be developed which will allow the rapid and quantitative detection of vitamin A-binding proteins. As an aid to the formulation of reasonable hypotheses for the function of the vitamin A-binding proteins, their localization within the retina and retinal pigment epithelium will be determined. In as much as the intracellular retinol-binding protein has already been demonstrated in RPE, its role in the uptake of retinol from serum will be studied. Experiments will be designed to test the hypothesis that serum retinol is transferred from the serum retinol-binding protein to the intracellular binder of the pigment epithelial cell. In addition, the role of vitamin A-binding proteins in the metabolism of the vitamin will be examined.